Background: Temperament is defined as a set of individual differences in behavioural tendencies. An extensive body of literature establishes the association between temperament and childhood psychiatric disorders and more recent studies have documented specific temperament profiles in infants with Autism Spectrum Disorder (ASD). Previous studies have found that infants and children with ASD, when compared to a control group, tend to have a particular temperament profile characterized by higher negative affect, lower urgency and lower effortful control, relative to peers who do not have ASD. However, little is known about how temperament varies within the ASD population and how that variability is associated with later outcomes, such as the development of adaptive skills, in children with ASD.

Objectives: The objective of this study was twofold: a) to identify subgroups of school-aged children with ASD with distinct temperament profiles; and b) to examine whether temperament subgroup membership mediates the relationship between ASD symptom severity and adaptive functioning outcomes.

Methods: Data came from the Pathways in ASD study, a large Canadian longitudinal study of children with ASD. The sample was composed of 185 school-aged children with ASD at T1 (mean age: 7.8 years; males = 155). Temperament profile was indexed using the T1 Temperament in Middle Childhood Questionnaire (TMCQ). Children were followed over a 3-year period (T1-T3, with T1 as the first assessment between age 7-8 years and one assessment every 12 months for 2 consecutive years). Seventeen TMCQ dimension scores were used in hierarchical cluster analysis to derive subgroups of children. A test of binary mediation was conducted to test whether the relation between T2 autism symptom severity (Autism Diagnostic Observation Scale; ADOS) and T3 adaptive functioning level (Vineland Adaptive Behaviour Scale; VABS II) was mediated by a child’s temperament profile.

Results: A 2-cluster solution was selected as the best fit to the data; the two clusters were characterized by distinct temperament profiles (for most TMCQ dimensions). Compared to children in Cluster 2 (60.5% of sample), children in Cluster 1 (39.5% of sample) had higher scores on activation control, affiliation, assertiveness, attentional focusing, fantasy/openness, and soothability, and lower scores on anger/frustration, impulsivity, discomfort, fear, sadness, and shyness. Children in Cluster 1 had significantly lower adaptive functioning skills compared to children in Cluster 2 (F(1,165) = 44.98, p < 0.01). The total direct effect of ASD severity at T2 was a significant predictor of adaptive functioning outcome at T3, before entering the mediator variable (t(161) = - 3.51, p <0.001). The mediation test revealed that the total indirect effect for temperament profile was significant (p < 0.001; point estimate = -0.16, 95% CI = -0.41 to -0.13), and influenced the relation between ASD severity and adaptive functioning outcome.

Conclusions: Study findings show that in school-aged children with ASD, distinct temperament profiles influence the relation between ASD severity and adaptive functioning outcome. These findings suggest that temperament may be a previously under-researched but important child-level characteristic to consider when investigating developmental outcomes and intervention mechanisms in children with ASD.